Electrical music system



March 21, 1933.

R. H. RANGER ELECTRICAL MUSIC SYSTEM Filed Dec. 30, 1929 8 Sheets-Sheet l INVENTOR R- H. RANGER W/ ATTORNEY March 21, 1933.

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' R. H. RANGER ELECTRICAL MUSIC SYSTEM Filed Dec. 30, 1929 8 Sheets-Sheet 2 INVENTOR R. H. RANGER ATTORNEY R. H. RANGER 1,901,985

ELECTRICAL MUSIC SYSTEM Filed Dec. 30, 1929 8 Sheets-Sheet 3 March 2], 1933.

INVENTOR R.H. RANGER BY 7 ATYLWNEY March 21, 1933. R RANGER 1,901,985

ELECTRICAL MUSIC SYSTEM Filed Dec. 30, 1929 8 Sheets-Sheet 4 70 KEY H INVENTOR R. H. RANGER ATTORNEY Eg 1-D March 21, 1933. R. H. RANGER ELECTRICAL MUSIC SYSTEM 5 NNN m a 3 Q. HF

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ATTORNEY March 21, 1933. R. H. RANGER ELECTRICAL MUSIC SYSTEM 8 Sheets-Sheet 6 Filed Dec. 30, 1929 INVENTOR R. H RMIGER BY 7 ATTORNEY R. H. RANGER 1,901,985

ELECTRICAL MUSIC SYSTEM Filed Dec. 30, 1929 8 Sheets-Sheet 7 March 21, 1933.

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H. RANGER ELECTRICAL MUSIC SYSTEM Filed Dec. 50, 1929 8 Sheets-Sheet 8 mvENToR R 4 RANGER 7% ATTORNEY Patented Mar. 21, 1933 UNITED STATES PATENT OFFICE RICHARD ROWLAND RANGER, OF NEWARK, NEW JERSEY, ASSIGNOR TO RADIO CORPO- RATION OF AMERICA, A CORPORATION OF DELAWARE ELECTRICAL MUSIC SYSTEM Application filed December 30, 1929. Serial No. 417,466.

My invention relates to a system for producing musical sounds. Broadly, the, invention relates to a sound producing apparatus or instrument of the t pe embodying constant frequency means or producing sounds as musical tones or notes of constant pitch, and variable volume and timbre for the particular note which it is to produce. In combination with such type of apparatus, I pro vide a system for selectively amplifying each of the produced notes or tones, so as to pro.- duce a composite note corresponding to each which will have the proper timbre and frequency characteristics.

Of course, I am aware of the fact that it has heretofore been possible to produce musical sounds through the aid of oscillators or frequency generators of either the audion or the enerator type coordinated with sound repro ucing instruments, and am also aware of the fact that it has heretofore been known in the art to utilize a system for producing musical sounds in which a high frequency source has been used together with a generator of variable frequency so as to produce by heterodyne action a resultant beat note of a frequency varying in accordance with the frequency of the note or sound which is de sired. In each of the systems of the type above described, it has also been customary to amplify either the frequency of the generator source or the beat note frequency so as to produce a well rounded-out tone such as may, for example, be clearly audible in large concert halls.

My invention, however, differs from what has heretofore been done in the art in that I employ a plurality of constant frequency tone sources for each of the plurality of notes comprising the musical scale so that each separate note, as it becomes audible upon amplification and by being directed through a sound reproducer, is formed from the fundamental frequency together with all of the other partials, harmonics, or modulating notes of appropriate interval to 've special effects, as minor amplitudes o thirds or fourths, suitable for producing the proper timbre, for example. These tones will hereinafter be referred to merely as the fundamentals (the partial of lowest frequency) and the other partials, or as the fundamentals and harmonics, or as the fundamental and over tones so as to avoid needless repetition of the above. With these tone producers I connect, in a manner to be hereinafter described, the reproducers or loud speakers for causing the generated frequencies to become audible.

My system also provides an especially flexible means by which the intensity of each of the harmonics or partials accompanying the chosen fundamental or first partial may be regulated at will so as to simulate the stop effects on the usual organ, such as, in one instance, perhaps to produce a note simulating a reed effect, while, at another instance, perhaps produce a note simulating a violin effect by proper regulation of the intensity or amplitude value of the various partials or harmonics accompanying the particular first partial fundamental. Still further, my invention has provided a system in which the tones or notes of the musical scale may be produced from absolutely constant frequency standards, and, in combination with these frequency standards, I may utilize what I have herein termed a selector system and a plurality of tone amplifiers, such that the sefector system prevents more than one single tone or note together with its partials or harmonics from being impressed upon one amplifier at the same time. Thus, the note reproduced at any one instant by any one amplifier and sound reproducer con,- tains only the basic and desired partial frequencies of the particular note chosen, and eliminates cross-modulation between a plurality of separate notes.

So far as I am aware, it has in the past been customary either to provide each note with a separate amplifier'or oscillator tube, or to combine all tones from all sources in a common amplifier, or to have a plurality of separately located amplifiers and sound reproducers so coordinated that only one of the plurality is used at any one time. The first of these systems has the disadvanta ethat an unusually large number of ampli ers or oscillators are necessary in order to obtain the desired results, and with them a great loss in efiiciency is experienced, and the second type of system has the disadvantage that, as above stated, several tones simultaneously 1mpressed upon a single amplifier or sequentially impressed u on a single amplifier cause, firstly, cross-modulation between various tones in the amplifier and thus produce distortion, or secondly, noises are produced in the amplifier by successively keying difierent tones or notes thereon prior to the time when the first tone has been cut off from the amplifier. In the production of pure tones of considerable amplitude, this cross-modulation is very serious. To avoid cross-modulation in a single amplifier, it is necessary to have great reserve power which is uneconomic'al.

My invention may further be characterized as being selective for the difierent notes played, somewhat similar to the selection of unused telephone lines with the automatic switching practice in telephone switchboards of today, in that it provides a separate amplifier for each of the notes that are to be struck simultaneously up to a predetermined maximum. Where more notes than the predetermined maximum are struck simultaneously, provisions are made to prevent sound reproduction from more notes than there are amplifiers. This limiting system will become apparent from the description which follows.

Careful research has disclosed that the number of separate notes which are usually played or struck simultaneously is limited and would rarely exceed ten for organ work, for example, assuming'that four notes ma be simultaneously played with each hand an one note played with each foot. However, for practical urposes and for convenience of illustration, l have merely chosen to illustrate my invention as capable of simultaneously producing six tones, but it should be understood that such illustration is merely given by way of example and not in a sense of limiting my invention to six notes played simultaneously, and I may, should I so desire, use more than six tones simultaneously (or less than six tones simultaneously) in accordance with conditions existing at any particular time.

To discuss further the utility of a plurality of separate amplifiers so that one amplifier is obliged to carry only a single note and the overtones, harmonics or partials accompanying or modulating it at the same time, the

advantages over a single amplifier are. many :first, no amplifier is absolutely linear,

of course, and the result of this is that one note is bound, therefore, to modulate another in the amplifier after they are combined in the amplifier circuits; secondly, unless all notes amplified at any one time are struck simultaneously, there is a tendency towards a scratching noise as the second note is brought upon the amplifier, due to the fact that the contact is not made instantaneously or is not made at a period of zero alternating current voltage upon the amplifier circuit. This scratching noise is not due to the direct current, as, of course, care must be taken to see that there is no direct current operated directly in the amplifier circuit, which would ive rise to distinct thumps, but is due to the eying of the tone frequency energy. As a third advantage of separate amplifiers for each note and a separate sound reproducer or loud speaker associated with each amplifier, it is obvious that any one amplifier can handle much larger volumes for any given note, if there is no need for a considerable amount of reserve energy to be available for other notes added thereon at the same time.

Therefore, as a primary object of my invention, I have sought to develop an electric organ system of the type herein described in which there is a separate amplifying means for each of the notes or tones simultaneously produced.

Another object of my invention is to produce an electric organ system which is capable of simultaneously playing any predetermined and desired number of musical tones or notes without experiencing interference between the several tones or notes.

Another object of my invention is ,to provide means for preventing any single amplifying system from being obliged to handle more than a single note or tone together with its partials at any one instant.

Still another object of my invention is to develop an electric organ system. in which means is provided for selectively keying an amplifier not then in use with any particular a note as the note is struck. V

A further object of the invention is to provide a system in whichthe lag effect of sound reproduction is reduced to a minimum by reason of sound generation which is entirely electric.

Still another object of my invention is to provide an electric music system in which the tones as produced by the tone generators includin the first partial fundamental tone and all desired accompanying partials or overtones may be keyed to appropriate amplifying systems prior to the time when the amplifier 1s keyed with the sound reproducer,

or, 1n other words, the sound reproducer keying is delayed until the tones are keyed, so as to avoid all objectionableefiects of keying noises and the like.

Also a further object of the invention is to provide a system by which the connection between the amplifiers and coordinated sound re roducers may be broken prior to the time w en the tones are removed from the ampli-.

fier so as to avoid all objectionable noises from keying and the like. In each of these last two named objects, the electrical contacts associated with each of the keys representing the diflerent notes of the musical scale are such that as the key representing the note which is to be played is depressed, the first connection so far as impressing the generator tones on the amplifier and sound reproducer is concerned will be to key the tones with the amplifier, and then at a later time through a delayed action system the sound reproducer is keyed to the amplifier; then, as the key is raised or released, the first operation taking place is the disconnection or disassociation of the sound reproducer and the amplifier, after which the generated tones in the form of the fundamental and chosen overtones are removed from the amplifier.

Another object of my invention is to provide an electric organ system such as is capable of playing each note or tone together with all of the harmonics or partials accompanying the particular tone or note.

Still another object of my invention is to provide a means for controlling the volume of each of the harmonics or overtones accompanying or modulating each particular fundamental note or tone in accordance with the character of the note or tone which it is desired to produce.

Still another object of my invention is to provide a means for accentuating any one part of the amplifier selection so far as the dilferent notes therein are concerned so that, for example, in one selection the bass or lower frequency notes' might be accentuated throughout, whereas, in another selection, the tenor or higher frequency notes might be accentuated throughout.

Still another object of my invention is to provide a means wherein I preferably coordinate particular amplifiers to particular groups of tones. That is, one amplifier may be particularly suited for the lower frequency tones, and another amplifier may be more particularly suited for the higher frequency tones.

Still a further object of my invention is to provide an electric organ system in which separate tremolos may be assigned to separate parts of the musical selection being played. This may be accomplished, for example, as will hereinafter he set forth, by changing the amplifying characteristics of the various amplifying systems in accordance with a predetermined schedule of changes.

While in many instances it is desirable to have the same tremolo effect for all ampli fiers and their associated sound reproducers, it should be noted also in connection with the tremolo that it is possible to rovide tremolos which are of different rates or different amplifiers, that is, for amplifiers carrying higher frequencies the rate might be higher, for example, than for amplifiers carrying the lower frequencies. To specify an example of tremolo operation which might be found suitable, a three to two ratio for high and low frequency amplifier tremolos has been found suitable where it is desired to produce a difl'erent tremolo effect for diiferent amplifiers, although it is to be understood that this ratio is merely illustrated by way of example and not in a limiting sense, since any desired and suitable ratio may be substituted where it is desired to have different tremolo effects on different amplifiers.

Still another object of my invention is to provide a system wherein the usual stop effects for producing different character notes may be conveniently regulated by merely changing predetermined resistance values, or other appropriate means suitable for controlling the current fiow in the ainplif ing circuits, so as to regulate the quality 0 the output energy from the amplifier through appropriate control of the intensity or amplitude relationship between the fundamental and the various artial frequencies.

Still another 0 ject of my invention is to provide an arrangement which will ermit the playing of notes not ordinarily nown or produced by the usual type of musical instruments. This, for example, might be accomplished by accentuating particular partials or harmonics of the basic frequency or even of entirely diliercnt notes added in controlled degree in order to differentiate from any usual character of note.

A still further object of the invention is to produce a system for representing or simulating a pipe organ in which the tone color is most flexible, due to the fact that it is possible to independently regulate the relative percentage of the various partials or harmonies with respect to the first partial fundamental note by varying the Volta e of the particular partial or fundamental requency im ressed upon appropriate tone amplifiers.

nether object of my invention is to provide an electric organ system or the like in which it is possible to gradually slide from one type 0 note into another type of note by controlling the resistance value, for example, in the amplifying circuit, in much the same manner as these values are changed for producing the usual stop effects.

Still a further object of my invention is to provide a means in which there is an extreme ease of regulating the temperament of the system, that is, the raising or lowering of the pitch of each note of the entire scale relative to the other, in accordance with the desired temperament, with minimum inconvenience.

A further object is to provide'a inusical system in which the pitch of the whole instrumentality may be raised or lowered to match the range of singers being accompanied or of instruments less flexible.

A further object is to provide a musical system in which the temperament may be modified from equal temperament to favor any given key.

Other objects of my invention are to provide an electric organ system which is totally or wood, or other types, or reproducing the notes. e

Other objects of my invention are to provide an electric organ system in which the objections of changes in pitch due to changes in circuit characteristics are substantially eliminated by the elimination of all oscillators or the like for producing the basic frequencies in which temperature or supply voltage changes produce changes in frequency.

Still another object of my invention is to utilize the various frequencies generated for the various notes comprising the musical scale in proper reduced intensity in order to provide for the harmonics or partials accompanying any predetermined basic frequency.

Still another object of my invention is to produce and provide an electric organ system in which the usual space requirement for setting up the arrangement is reduced to a minimum by providing compactly arranged switching and selecting circuits, together with a minimum number of amplifiers and associated standard frequency tone producers, and to eliminate totally the objectionably large number of pipes used to produce the desired sound efi'ects.

Also as a further object and advantage of my invention, I seek to provide an electrical music system in which the usual blowers, assuming the system is an organ, for producing vibration in the organ pipes are eliminated by substitution of the tone generators and coordinated loud speakers or other appropriate sound reproducers.

Still another object of my invention is to provide an electric organ system in which the mechanical driving means for the various tone or note producers may be reduced to a minimum.

Still other objects of my invention are to provide an electric organ system such as is relatively simple in its construction and arrangement: to provide an electric tone producing system which when once installed is substantially free from the need of attention so far as tuning adjustments and the like are concerned because of the substantial independents of tone change with any change in temperature; and to provide an electric tone producing system which is efiicient in its use, compact in its arrangement, easy to install, conveniently operated, substantially fool-proof in operation, and readily set up.

Still other and further objects of my invention will become apparent and at once suggest themselves to those skilled in the art to which the invention relates by making reference to the following specification and claims in connection with the accompanying drawings, wherein:

By way of diagrammatic illustration of a ortion of my invention, I have illustrated y Fig.1 an arrangement consisting of three keys of my organ and one amplifier associated therewith. In Fig. 1 of the drawings, Fig. 1A constitutes the upper left hand corner of the drawing to the right hand portion of which is attached Fig. 1B; immediately below Fig. 1A, the arrangement shown by Fig. 1-C is to be connected; to the right of Fig. 1-C and beneath Fig. 1B the portion shown by Fig. 1-D is assumed to be connected; and, the amplifying system shown by Fig. l-E is connected to the amplifying connections from Fig. 1-D:

Fig. 2 illustrates a modification of the means for producing varying tone effects from that shown by Fig. 1-Ez Fig. 3 illustrates a modification of the amplifying system (also assumed to connect to the amplifying connections of Fig. 1D)

from that illustrated by Fig. 1E, to illustrate the application of alternating current types of amplifying tubes to the system;

Fig. 4 illustrates a modification of the tone producing arrangement from that shown by Fig. 1-A, wherein Fig. 4rz illustrates a side view of a single tone wheel and the signal or tone pick-up means therefor, and Fig. 4b illustrates a top view of a similar tone wheel;

Fig. 5 illustrates a complete assembly of a plurality of tone generating wheels in which. a turbine drive is used for rotating the tone wheels, and with this an appropriate form of speed governing means is illustrated;

Fig. 6 illustrates a similar tone generator wheel arrangement to that shown by Fig. 5,

but shows an electric drive as being substituted for the turbine drive of Fig. 5; and,

Fig. 7 illustrates a preferred form of synchronizing system for use in connection with the tone generator wheel driving means of Fig. 6.

In accordance with the arrangement herein set forth, and in order to accomplish the purposes and objects of my invention by one of many suitable arrangements, for the purpose of diagrammatic illustration, a. relay setup is used to show my invention. For convenience, the keyboard of the organ, usually consisting of sixty-one separate notes, is arbitrarily divided into two parts at middle C at, for example, substantially 262 cycles, upon the basis of middle A being at 440 cycles in the octave above this C. In accordance with the present disclosure, three amplifiers work from middle C downward and c011- stitute the left side'of the system, as shown in the drawings. In order to complete the set-up, another set of three amplifiers works for all of the notes on the keyboard from the same middle C upwards, and are connected in identical manner to that shown in the drawings, but have not been herein illustrated for the purpose of convenience.

Similarly, separate amplifiers are rovided for the purpose of reproducing t '0 notes played by the organ foot pedals. The selection to be desired in an instrumentality of this type may work, for example, in the following manner, although not necessarily limited thereto. The first amplifier should preferably always be set to work on the first note struck on the left side, the second amplifier arranged to work with the second note struck, and then the third amplifier to work with the third note struck. As has been above stated, with the arrangement shown for the purpose of illustrating my invention, onl three notes played by each hand can simu taneously be accommodated in the amplifiers. If two notes are to be struck simultaneously, provision must be made for keying each of these notes with a particular amplifier, and, therefore, I have arbitrarily assumed that the lower frequency note struck will play on the first amplifier, and the next note struck, that is, the note of higher frequency and nearer towards the C note, which, as above stated, was chosen as the dividing point, will play on the second amplifier. imilarly, if three separate notes are struck simultaneously, the third note towards C will play on the third amplifier, with the first two playing as :eviously stated.

or the right hand side of the system, not illustrated, the selection, according to the arbitrary system of operation to be herein described, should work in exactly the opposite direction; namely, if three notes are struck simultaneously. the highest note struck or the one furthest away from middle C will play on the first amplifier on the right side, the second one down toward C will play on the second amplifier, and the third one down toward C will play on the third amplifier. The purpose of the relays and amplifiers is thus seen to be that of selecting and amplifying appropriately the given notes desired, while the individual tones are produced extraneous to these arrangements.

Since in many cases it may be desirable to play more than three notes near the center of the keyboard, it is possible to dovetail the left andright hand relays so that each set ore :laps and thus provides a means wherebv the entire number of notes to be played simultaneously may be played within a close range of frequencies or notes on the keyboard. In many cases, it is advisable to have only a very few notes capable of being played by amplifiers and reproducers coordinated with the relays for each side or end of the keyboard. By this means the system may be so interlocked that the last two or three notes to the left and right of the keyboard may be played only through a single reproducing C3 system, and thus conserve relays. Of course,

under the last named condition, care should be taken to make certain that it would never be necessary to lay more than one note at a time at the en s of the keyboard, because, if it were, one note would be lost, in the sense that it would not be reproduced.

In order to produce these various tones, it is, of course, possible to use several different arrangements. For example, I may use, where desired, air driven tuning forks, one fork being provided for each note of the scale desired. Air driven tuning forks are preferred to electrically driven forks for the reason that there is a total freedom from se arate vacuum tube drives for eachfork with the consequent large amount of electrical circuits and energy. Of course, the forks may be of either the steel or the quartz type since in utilizing an air drive, it makes no difference whatever as to the particular type of fork so far as convenience of driving the same is concerned.

In another arrangement, I may, where desired, use tone wheels which consist of a series of wheels each of which is provided with teeth adapted to complete an electric tone generation circuit either through electromagnetic or electrostatic means. The number of teeth on each wheel is different so that as the series of wheels is rotated the progressive chan e in the number of teeth gives the efi'ect o the same notes in different scales. To produce the other notes in each scale and for the complete series of scales similar sets of toothed wheels are used, or, in other words, there are twelve difierent sets of wheels to produce the tones corresponding to the tones or semitones of the octave. Now, to produce the different frequenc notes the corresponding wheels forming eac complete set may all be of the same number of teeth and rotated at different speeds, or all of different number of teeth and rotated at the same speed. However, for convenience of installation, the former has been found more suitable.

Also, the various tones produced may be produced by piezo-electric bodies, or, in fact, all types of crystalline bodies which may be caused to vibrate at constant frequencies.

In addition toeach of the types of tone producers of constant frequency above set forth, I may roduce tones electrically without the liability of distortion and noise by providing photo cells and associating therewith chopping disks interposed between the source of the light directed to the photo cell and the cell itself. In such a case, the chopping disks may be provided with holes therethrough arranged about their outer margin so as to interrupt periodically the light reaching the cell at the frequency corresponding to the note which is to be produced, for example, of the general type shown by my Patent No. 1,789,687, granted January 20,

1931. With such an arrangement, it is, of course, possible to use a single photo cell for ouch of the notes, and by properly arranging a plurality of sets of openings in the light chopping disk in paths concentric with each other (as is also shown by said above named application) cause each photo cell to produce only an electrical output corresponding to the exact frequencies desired, toether with only the particular harmonics which are to be coordinated therewith for the purpose of rounding out the tone or timbre produced from the particular note in the individual speakers as they are successively coordinated therewith as each separate key corresponding to each photo cell frequency is depressed on the keyboard.

In each of the above cases, it is the frequency of the generated tone, and not the sound itself. as for example the sound of the vibrating forks, which controls the reproduced tone output of the sound reproducer connected with each of the amplifiers.

To refer now to the drawings forming a part of this specification, a key I is shown at the lower right hand corner of Fig. 1C, and this key, for example, may corres ond to the note C having a frequency 0 approximately 65.4 cycles. According to the showing of the drawings, the keys I, II, III, etc. are each intended to represent one of the plurality of keys of the usual organ console. Beneath each ey, in the usual manner of connecting electric contacts, I have provided the switching contacts to be hereinafter described. In this manner all of the switching associated with the key for the purpose of selectively keying the various amplifiers is contained beneath the various keys and is out of sight.

As shown by the accompanying diagram, for example, the note 0, wh ch may be as sumed to be equal to 65.4 cycles, may be generated by means of a tuning fork 2 (Fig. l-A). This fork 2 may be of either the steel or quartz type and driven by air in any desired and appropriate manner. for example. in accordance with the principles shown and described in United States Patent No. 1,831,- 638, granted on November 10, 1931 jointly to me and to C. E. Nelson. Energy generated through the vibration of the fork may be electromagnetically picked up through the use of the horseshoe-shaped magnet 3 surrounding the tine 4 of the fork and having a coil of wire 5 surrounding the same. One terminal of the coil 5 is preferably grounded at 6 and the other terminal connected to a terminal of the relay or selector system. as will hereinafter be described. The function of the key I is to supply positive current derived from a source of energy connected to the terminals 7 and 8 to the separate pa r of wires 9 and 10 connected with the bank of relays. These relays function to serve as a p rtion of a selector system to selectively key the various amplifiers, to be hereinafter described with the tone producers and those relays associated with the key I are indicated as R R R and R in which, for convenience of reference, the last numeral of each is a 1, while those associated with key II are indicated with numerals ending in a 2, etc. These contacts are then made by depressing the key I and causing it to close contacts 11 and 12 so that current from the source 7 may be passed, for example, through resistance 13, choke coil 14, the resistor 15 through the contact arm 16, the contact 11, the lower portion 17 of the key I and the conductor 9 to one of the armatures of the relay systems R R and R or, upon further depression of the key, from the terminal 8 to the choke 18, the terminal 1.9, the contact arm 20, the contact 12, the contact arm 21, through to the conductor 10 connecting with one of the various contact points hereinafter termed the keying contacts and later described in connection with the operation of the relays R R and R Thus, as the key is depressed current first flows through conductor 9 and later, as the key is further depressed, current flows through the conductor 10 to the keying contacts of the various relays.

The first horizontal row of relays R R and R etc., are what will hereinafter be termed starting relays, and are respectively coordinated with the keys I, II, III, etc. These relays act whenever a key associated with the particular unit note is played, and their purpose is to select one of the relays shown in the vertical row of relays above each note that is not otherwise busy, for the purpose of transferring the tone to the amplifiers, as will hereinafter be explained. For the purpose of illustration, it will now be assumed that key numbered I, assumed to correspond to the note C, is the first key to be struck in the system and that it alone is struck. According to the above outlined requirement, it must, therefore, select the relay R as the one that will place the required tones into the first amplifier A, shown to the right of this relay by Fig. 1E, which will lead to its particular loud speaker or tone reproducer, not shown but which may be of any known type, such as dynamic, magnetic or electrostatic.

That this is done is seen by following diagram of connections from a view of Figs. 1-0, 1A, 1D, and 1E combined. Now, assuming the key I to be depressed or closed, current from the source connected at 7 and 8 flows through the lower portion 17 of the key I through the conductor 9, the conductor 22 to the armature 212 of relay B through conductor 22' to the armature 312 of relay R through conductor 22" to the armature 412 of relay R through conductor 23 and thence back to the relay R which it operates,

to close the several armatnres thereof, and then to ground at 24. The relay R is preferably shunted by a capacity 25.

As shown, all of the relays are indicated in their off position and the relay coil R; operates all of the armatures shown immediate- 1y to the right thereof, such as 26, 27, and 28; the relay R operates all of the armatures shown immediately to the right thereof, such as 211 through 219 inclusive, and, relays R and R likewise close all of the armatures to the right thereof during periods when current is passed therethrough. As the relay winding R is energized, the armatures 26, 27 and 28 are closed against the contacts shown on Fig. 1-C as immediately to the left thereof. As the armatures 26, 27 and 28 are closed, the only one of these which has current on it is the armature 26, which is because the relay R as shown, is in what may be termed a spacing position, and has its armature 202 resting upon the contact to the right thereof to supply positive current from the positive source connected at 29, through the conductor 30, the armature 202 and associated right side contact, the conduetor 31, the resistor 32 and the choke 33 to the armature 26. The purpose of the resistance and choke is to keep the current wave front to a gradual slope rather than to a steep front, which would act to cause interference on amplifiers that are already working. The resistance and choke have, however, no function in the straight selection operation for keying the different amplifiers as the tones are selectively applied to the selector system.

Now, when the relay R contact or armature 26 moves to the left so as to rest against the left side contact point, positive current coming from the source 29 through the armature 202 may be traced up directly to the right side of relay R through the armature 26 and the conductor 34 so as to cause relay R to close all of its associated armatures upon the left side contacts by reason of the current flowing from source 29 through the relay R to ground at 35. This closing of all of the armatures of relay R to the left will then cause the positive current coming from the key I through the conductors 9 and 22 to then flow through the relay R to control the same directly without the intermediary of the relay R At the same time, the closure of relay R 1 will break the circuit previously described through the right side contacts of armatures 212, 312, 412 of relays R R and R for operating the relay R as the operating current for the relay R, passed through the conductor 22 upward through the armature 212 of relay R and the right side contact thereof, then through the conductor 22' and the right side contact of the armature 312 of relay R the right side contact of the armature 412 of the relay R and thence down through the conductor 23 to the relay R to ground, when the armatures of relay system R rested on the right side contacts, or in their non-operating position, as shown.

Since in the operation of the relay R all of the armatures are moved to the left, as above described, the closure of the armature 211 upon the left side contacts opens the ground circuit of all of the relays R R etc., to the right of relay R which otherwise passed through conductor 86', the choke 36 to ground at 35 so that now none of these relays R R etc. to the right of R can operate no matter what other keys are depressed, since the circuit connecting each of these relays is now open. This effectively prevents any other relay in line (horizontal line as shown) with the relay R such as R R etc. for example, from closing tone currents into the amplifier system A to the right thereof, and likewise fits in with the previous stipulation set forth above in the general statement of invention and objects thereof that when more than one key is depressed at a time, the amplifier A will be worked only by the first note to the left of middle C that is layed.

Armature 211 when actuated by relay R to move to the left-side contact point closes a circuit to ground at 35 through the choke 36, the armature 211 and the left side contact thereof through to the conductor 37 and thence through relay R to the positive potential source 37, so as to close the armatures 201 and 202 of the relay R over upon contacts to the left from the position shown. This actuation of the relay R and the movement of the armatures 201 and 202 to the left breaks the circuit from the positive potential source connected at 29, through the armature 202, the contact to the right thereof, the conductor 31, the resistor 32, the choke 33, the conductor 38 to the armature 26 of relay R and thence through the right side contact of armature 26 through the conductor 39 to the armature 40 of relay R and its right side contact terminal, the. conductor 41, the armature 42 of relay R and its right side contact, etc. This arrangement of cascading armatures 26, 40, 42, etc. to the right of the relays R R R etc., likewise carries out the provision set forth in the statement and objects of invention that if more than one key is operated at the same time, it will be the relay to the left that carries forward its operation first.

Likewise, when the relay R operates, it closes the armature 201 against the left side contact thereof so that positive current from the terminal 29 may flow through the conductors 30 and 44 through the armature 302 in its position of rest against the right side contact thereof (as shown by Fig. 1-A), and

ture 301 of relay R thence down through conductor 45 to resistor 46 and associated choke coil 47, conductor 48, through to right side contacts of the armatures 27, 50, 52, etc. through conductors 49,

51, 53, etc. respectively. This provides that if key II, arranged similarly to key I and connected to the conductors 54 and 55 is closed or depressed, it will operate the relay R by causing current to flow from conductor 54, through armature 222 and its right side contact of relay R and from there through conductor 56 through the right side contact of armature 322 of relay R to conductor 57, to the armature 422 of relay R from the right side contact of which it flows through conductor 58 to the winding of relay R and thence to ground at 59, in a manner similar to that hereinbefore described in connection with the key I operating the relay It Now. bearing in mind the fact that, as above described, the relay R has been actuated to move armatures 201. and to the left, so that positive current from source 29 can now flow through armature 302, conductor 45, resistor 46, choke 47, conductor 48, armature 27 of relay R conductor 49 to armature 50 of relay R and that no current from source 29 can flow through armature 202 of relay R to armatures 26 or 40 of relays R, or R and that relay R has not yet operated so that no current can flow toward the armature 402 of relay R because armaforms a break in the circuit, it follows that current from the source connected at 29 may flow through armature 50 of relayR closed now upon its left side contact, through conductor 59 to actuate relay R by flowing through the winding thereof, the conductor 60, the armature 311 of relay R which rests upon the right side contact, to the inductance 61 and to ground at 62. Thus, it is apparent that relay R is operated in the same manner as was relay R when the key I was depressed. \Vhen relay R operates, it clears relay R by breaking the circuit from the positive source connected through key II to conductor 54 by moving the armature 322 away from the right side contact. Likewise, the closure of relay R operates relay R through the movement of armature 321 to the left and upon the left side contact thereof, so that a circuit is closed from the source of positive potential connected with relay R at terminal 63; through the relay R20; through conductor 64 from relay R to the left side contact of armature 321; through armature 321 resting on the left side contact, and thence through conductor 60, and inductance 61 to ground at 62.

Thus, the operation of relay R moves armatures 302 and 301 to the left and breaks the circuit previously completed from source connected at 29 through armature 302 to armatures 27, 50, 52, etc. In a manner similar to that above described for supplying current to armatures 27, 50, 52, etc., when the armatures 302 and 301 of relay R move to the left so that armature 301 closes on its left side contact current from thesource connected at 29 flows through the conductor 30, the armature 201, the left side contact thereof, the conductor 44, the armature 301 and its left side contact to the conductor 65, to the armature 402 of relay R and its right side contact to conductor 06, resistor 67, choke 68. and conductor 69, to the armature 28 of relay R and the right side contact thereof, thence to conductor 70, armature 71 of relay R and the right side contact thereof to conductor 72, to the armature T3 of the relay R, and the right side contact thereof to operate one of the various tone selecting relay systems for the third key to the right that is pressed.

Assuming that key III is the third key to be operated (which, of course, would probably not do for harmony, but is illustrated by way of example) then the relay R operates in like manner to the relays R and R and this in turn operates the relay R through armature 431 and the left side contact thereof and conductor 76 which clears the entire side of the system, as shown, and prevents any other note playing until one of these three notes represented by the keys I, II and III is released.

Now, to give a concrete example of this illustration, it will be recalled from above that the depression of key II caused the action relay R to move all armatures 40, 50 and 71 to the left. Then, with armature 50 moved upon its left side contact, and since relay B was in locked position with its armatures moved to the left, current flowed from source 29 to actuate the relay R Then, as relay R was closed, the relay R was released, While relay B was closed. Under this condition the energy to keep relay R closed was derived from the source (not shown) connected with conductor 54 through the depression of the key II, due to current flowing from the positive source connected with conductor 54 through depression of the key, through the conductor 54, to the armature 322 of relay R and thence through the left side contact of armature 322 through the relay winding R the conductor 60, and choke 61 to ground at 62. Therefore, so long as key II is depressed, the relay R must remain in closed position.

owever, as the key II is raised the circuit from the positive source connected through conductor 54 and the armature 322 to ground is broken and relay R opens. As relay R opens the armatures all move to the right (to the position shown by the drawings) As this happens, the circuit from the positive source 63 connected to relayR and to ground at 62 through armature 321 and the left side contact thereof is broken and the "locking relay R also opens. When this happens the armatures 301 and 302 move to the right to the position shown by Fig. 1-A of the drawings, and positive current will now be supplied from the source connected at 29 through armature 302 to the middle armatures 27, 50, 52, etc. of relays R R R etc.

In the operation previously described, the only relays of the selector system which are now assumed to be closed are relays R and R and these are kept closed due to the depression of keys I and III. Thus, all of the relays in a vertical line above the key II are in open position. Likewise, this is true of the corresponding relays associated with all other keys in the left hand register of the scale correspondin to other notes (neither relays nor keys being shown due to repetition of circuits), so that as any key is depressed (of course excepting ke s I and III already depressed) a circuit will e closed to actuate rela 5 R or other similar relays coordinated with the other keys.

As this happens and since current is supplied to all of the middle armatures 27, 50, 52, etc., one of the keying relays in a horizontal line with relay R will be closed and the relay R will again be actuated, as before, so that an additional tone will be impressed u on the amplifiers, as will hereinafter be ascribed.

To show now how the selection system would work if the order of depression of the three keys illustrated by way of example were changed, let it be sup osed that key III is first depressed, then rey I, and then key II. Under such conditions, and in accordance with the above set forth description, selector relay R would first operate, then relay R and then relay R Thus, by varying the order of depression of the various keys the relay system which operates in the vertical line above each key (as shown) for selection purposes may be changed, and, ac-

cordiiigly, as will hereinafter appear, the P amplifier coordinated with the particular tone will be different. ,1;-

The purpose of the contacts or armatures of the various relays which end in the numeral 3 for each tone relay, such as 213, 323 and 433, for example, on relays R R and R respectively, is to provide a charge on the capacity elements 77, 81 and 85 through resistors 76, 80, and 84 and conductors 79, 83 and 87 so as to hold the relays R R and R (assuming notes I, II and III were played, as above described) closed for a slight time interval after any of the keys I II or III are released. The reason for such an arrangement is to provide a short time interval after release of the keys for the remaining circuits to clear the tones out of the ampllfier before new tones produced by depressing other keys are impressed upon the input to the amplifiers.

In addition to the armatures already mentioned as being associated with and forming a part of all of the relays such at R R R R etc., for example, there are six other armatures provided on each keying relay. Thus, rela R for example, is provided with additional armatures 214, 215, 216, 217, 218 and 219; relay R is provided with additional armatures 324, 325, 326, 327, 328, and 329, etc., and, upon current flowing through the various relays, such as R and R for example, all of the last named armatures will move to the left from the position shown by the drawings so as to rest u on their associated left side contacts. 0 these various armatures, for purposes of identification as to function, I have termed all of the armatures ending in numerals 4, 5, 6, 7 or 8 the tone contacts and all ending in the numeral 9 as the keying contacts.

Each of the armatures identified as the tone contacts is connected with one of the particular tone generating elements as, for example, a tuning fork, as shown by Fig. l-A. In the arrangement shown, provision is made for producin a resultant note in the output of the amp ifiers, to be hereinafter described which will be composed of the basic or first partial fundamental frequency of the note played and, in addition, four other partials or harmonics. Thus, makin reference to the note 0 assumed to be playe by depressing the key I, the note played will include the tone produced by the vibration of the fork 2, producin the fundamental; the tone roduced from t e vibration of fork 88 as pic ed up in the pick-up coil 92 grounded at 96 similarly to the pick-up coil 5 of fork 2, forms the next partial or first harmonic for this note; the tone impressed upon ick-up coil 93, grounded at 97, from the viration of fork 89 forms the succeeding partial or second harmonic; likewise the tone icked up in the coil 94 rounded at 98, of the fork 90 formsthe f0 lowing partial or third harmonic; and, similarl e uppermost partial or harmonic use in the tone production is produced in the coil 95, ounded at 99, through vibration of the or]: 91.

Confining the explanation of the tone production to the note correspondin to key I, for example, the tones produced t rough the vibration of forks 2,88, 89, 90 and 91, as impressed upon the pick-up coils 5, 92, 93, 94 and 95 are transferred to the.,terminals 100, 101, 102, 103, and 104 of they selector system above the key I through conductors .105, 106, 107, 108 and 109 respectively. When the tones from the various tone generators 2, 88, 89, 90 and 91, for example, as impressed upon the terminals 100, 101, 102, 03 and 104, they are simultaneously impressed upon the particular armature of the various relays R R and R coordinated and connected with these terminals. Thus, through conductor 110, the tone applied to terminal 100 from fork 2 is simultaneously applied to each of the armatures 414, 314, and 214 of relays R R and R respectively. In the event that none of the relays R R or R are closed (opposite position from that shown by Fig. 1) there is no place for the electrical ener y generated by the fork to flow, because t e right side contacts upon which the armatures 414, 314 and 214 rest with the relays open are blank, and, therefore, while the tone is generated, it is put to no useful purpose.

Similarly, tones produced by forks 88, 89, 90 and 91 are impressed upon contacts 101, 102, 103 and 104 are directed through conductors 111, 112, 113 and 114 to the sets of relay armatures 415, 315 and 215; 416, 316 and 216; 418, 318 and 218; and 417, 317 and 217 respectively, all of which are also in open position and resting upon the blank right side contact unless a note is played.

As any one of the keys I, II or III is depressed, and assuming for purpose of illustration that the key depressed is the key I, the operation of which was first described, then, as has been above set forth, the relay system R is actuated and all of the armatures 211, 212, 213, 214, 215, 216, 217, 218 and 219 are closed so as to rest upon their left side contacts (see Fig. 1-(3). Under such conditions, of course, due to the interlocking feature hereinbefore described, it would be impossible for the relays R or R to close, and, of course, when it is the tone from the tone corresponding to the fundamental and the chosen partials for the key I which is desired, it is obvious that there would be no reason for impressing these tones upon more than one relay in the selector system.

Now, as the relay R has closed and tones impressed from the forks coordinated with the ke I, as above described, are impressed upon t e armatures 214, 215, 216,218 and 217, a circuit will be completed through conductors 115, 116, 117, 118, and 119 connected respectively to the left side contacts of the relays 214, 215, 216, 217 and 218.

Each of the conductors 115, 116, 117, 118, 119 is connected to an amplifying system designated as A, to be hereinafter described. Similarly, if the relay system R were closed, then the tones corresponding to the note coordinated with the key I would be impressed upon similar conductors 115', 116, 117, 118' and 119' through the armatures 314, 315, 316, 317 and 318, and, likewise, if it were the relay R which were actuated instead of the relay R the tones would be impressed upon 1: e conductors 115", 116", 117", 118" and 119" in a similar manner, only in the latter two cases the conductors connected to the armatures of the relays B and R would be respectively coordinated and connected with amplifying systems designated as B and C respectively.

In this connection, it should be noted that all of the relays in a horizontal line with relays R R and R are coordinated with the same amplifier. Thus, all relays in the horizontal line with relay R are coordinated with the amplifier A; those in the horizontal line with relay R are coordinated with the amplifier B and those in the horizontal line with relay R are coordinated with the amplifier C.

As the arrangement is shown, it appears that each of the forks 2, 88, 89, 90 and 91 are used only for supplying the fundamental and partials for the key I, but this is merely for convenience of illustration, since it should be borne in mind that while the fork 2 furnishes the fundamental for the note corresponding to the key I, it may also furnish one of the partials for some other note coordinated with any other key, and, similarly, to consider the fork 89, for example, this fork is indicated as generating the second partial of the fundamental shown coordinated with the key I, but likewise this fork having a predetermined output frequency may furnish the fundamental for some other note coordinated with any other particular key chosen, and at the same time, may also furnish one of the partials for some other key. Therefore, by a careful analysis of each tone comprising the usual sixty-one tones or more notes of the organ keyboard, it is possible to so coordinate each of the different tone generators as to have them function both as generators of the basic or fundamental frequency for the particular notes and also as generators for the harmonics or partials coordinated with various other notes.

Thus, for example, it might be possible to also connect the pick-up coil 93 of the fork 89 through the conductor 107 with another terminal such as 130, for example, connected with the key III so that in this case the fork 89 would furnish the fundamental tone for this key. This illustration is given merely by way of example and not in any limiting sense so that the application of the invention will be more readily understood, but it should be further understood that in an arrangement of the type which I have devised and developed, there will be a fundamental (a first partial) and four other partials for each note and that there will be provided in the system tuning forks or other tone generators of an appropriate number, so that all of these fundamentals and partials may be produced.

Under such conditions, and assuming that relay R is closed due to the depression of the key I, the tones impressed thereon from the tone generators will pass as electric currents along the conductors 115, 116, 117, 118 and 119 to one of the amplifiers, such as amplifier A, to be described. The currents flowing in the conductors are impressed on the primary windin of the audio transformers 140, 141, 142, 143, 144 and 145 through resisters, which may be, for example, in the form of potentiometers 146, 147, 148, 149 and 150. Thus, current corresponding to each partial and the fundamental flows from one side of each potentiometer through a conductor 151 to gpound at 152 to complete the 1 tone circuit. ere it should be noted that the fundamentaltone coming from the fork 2 as a tone producer and through conductor 115 is applied to the primary winding of both of transformers 140 and 141, being impressed directly on transformer 140 and through the potentiometer 146 or. transformer 141. This serves to provide for better regulation of the fundamental tone than if it were supplied to only a sin le amplifying tube.

The secon ary of each of the transformers 140, 141, 142, 143, 144 and 145 is connected to vacuum tube amplifiers 153, 154,155, 156, 157 and 158 respectively of the triode type (for example in D. C. installations, a tube of the type known in the art as the UX-207-A). The grid electrode of each tube is supplied an appropriate bias potential from a bias battery 159. One side of the filament member (preferably the negative) of each amplifiyi'ng tube is grounded at 160 through a con uctor 161. ppropriate filae ment current is supplied to each tube from a positive source connected at 162 and is preferably regulated independently for each tube by means of the usual filament rheostat 163. Plate current from a source of positive potential connected at 164 is supplied through the choke 165 to conductor 166 and thence through conductor 167 to the plate electrode of all the aforementioned tubes, which, as is a readily seen, are connected with their outputs in parallel.

In well known manner, the tones impressed upon each of the amplifiers 153, 154, 155, 156, .157, and 158 are amplified and impressed, due to the parallelly connected outputs through conductors 167 and 166 and ca acity 168 upon the primary windin 169 of t e transformer 170, from t e secon ary circuit 171 of which the energy is directed to a pair of ush-pull connected amplifiers 172 and 173. he pushpull connected am lifiers 172 and 173 have their grid electro es appropriately biased throu a biasing battery 174, and one side of the filament of each tube is grounded at 175. To the other side of the filament appropriate filament current is supplied from. a source connected at 176 in a manner to be hereinafter described.

Thus, it is seen that as tones corresponding.

to the tone frequencies of the se arate sources reducing the fundamental an accompanying partials of the notes which it is desired to reproduce are impressed upon the amplifiers "carried over and the armature 202 to the rela 153, 154, 155, 156, 157 and 158, and are then through the transformer 170 to be impressed upon the amplifiers 17 2 and 173, it is necessary to provide some means for keying these amplifiers as the tones are impressed. Accordingly, I have provided a means by which the amplifiers 17 2 and 173 may be ke ed through their plate circuits.

0 refer back to the relay system R and the armatures associated therewith, it should be understood that as the relay is actuated, the armature 219 closes (of course assuming that note I is played and current from the source 8 may then ow through the choke 18, the terminal 19, the contact arm 20, contact 12, the contact arm 21 on the key I, the conductor 10, the left "side contact of the armature 219 and the conductor 177 to the terminal 178 where it passes through the conductor 179, the armature 202 of the relay R through the right side contact 180 of the armature 202 and the conductor 181 down through the relay R to ground at 182. Thus, seen that as current flows through the armature 219, it is the current flowing causes the relay R to operate. As the relay R operates so as tomove the armatures 201, 202 and 203 to the left, the circuit connection through the conductpzr 179 40 is broken. Current is now adapted to ow from the same source 8 throu h the same conductors previously describe to the terminal 178, and, due to the open circuit through the conductor 179, current now flows through the resistor 183 (which had previously been shortcircuited by the conductor 179) and the conductor 181 so as to keep the relay R in closed position against the left side contacts. Due to the drop in voltage of the current passing through the resistor 183, the current now operating to keep the relay in closed position merely serves as a holding current and barely holds the relay armatures open and away from their right. side contacts.

As the relay R is actuated by current flowing through the conductor 177, and either through the armature 202 for initial closure or through the resistor 183 for holding, the

armature 203 is moved to the left from the position shown in the drawings. Under such conditions plate current from the source connected at 184 may then flow through the conductor 185, the left side contact 186, through the armature 203 and theconductor 188 to a terminal point 189 connected between a pair of resistors 190 and 191, and flows through the resistor 190 and the choke 192 to the midpoint 193 of the primary winding 194 of the transformer 195. The current reaching the point 193 then divides through each half of the primary winding 194 to furnish plate current for the tubes 172 and 173.

It should be noted that the relay R, has inshunt therewith a capacity element 196 for the purpose of reducing any sparking efiect.

Also, a capacity element 197 is placed in shunt with the series connected resistors 191, 190 and the choke 192 for the purpose of smoothing out the plate current to reduce the steepness of the current wave front. This tends to reduce any possible key thumps. Likewise, with the vacuum tube amplifiers 172 and 173 connected in push-pull fashion, as shown, the thump will be materially reduced if the tubes, which may, for example, be of the type known in the art as the UX120, are, for this action, carefully matched as to their operating characteristics.

When the relay R igain opens due to the key I being raised, due '0 a release of pressure thereon for example current supplied from the source 8 to actuate or hold the relay in open position is cut ofi and a short circuit is placed about the resistor 191 by the closure of the amarture 203 upon the right side contact 187. At the same time plate current from the source connected to 184 is cut off from the amplifiers 172 and 173. With the armature 203 resting against the right side contact 187 of the relay R so as to short circuit the resistor 191, the tube plate current is reduced to zero much more quickly than would otherwise be the case because this arrangement provides a connection between the resistor 190 and ground at 240 through the conductor 210.

With plate current supplied to the tubes 172 and 173, as the various keys which are to be coordinated with this amplifier are played, it is apparent that current will flow through these tubes and through the transformer 195 from which it ma be impressed upon the transformer secon ary 198 and further amplified through the tubes 199 and 200. The grid electrodes of the tubes 199 and 200 are appropriately biased from a source 204 connected to a point on the resistor 205. A capacity element 206 having one terminal thereof connect to one end of the resistor 205 and the other connect to a point on the filament rheostat 207 shunts the resistor and a part of the filament rheostat. Filament current is supplied to these tubes in any appropriate manner from a source of filament potential connected at 208, for example, and grounded from the other side of the filament at 209.

The output energy from the push-pull connected tubes 199 and 200, which may be, for example, of the type known in the art as the UX842, is then fed through conductors 241 and 242 to the primary winding 243 of the transformer 244 to which plate current is supplied at the mid-point of the primary from a source of plate potential connected at 245, for example. As current flows through the transformer 244, electrical energy is then transferred tothe transformer secondary winding 246 to actuate a loud speaker system (not shown) connected to the terminals 247 and 248.

In order to produce the tremolo effect previously outlined in connection with the state ment and objects of invention, amon the various systems which may be used, it has been found convenient to provide a system for cyclically and continuously changin the filament current supplied to the amp ifiers 172 and 173 for the purpose of controlling the electronic emission thereof and thus changing the amplifying characteristics of the tube so as to increase and/or decrease the output thereof, or, in other words, increase and/or decrease the input to the coordinated sound reproducer according to a predetermined schedule. Of course, other embodiments may be found suitable for producing this tremolo effect, and while I herein describe one means by which this may be accomplished, I believe myself to be entitled to make and use any and all modifications such as fall fairly within the scope of the present scheme, which might, for example, be done by variations in grid control bias current, by appropriately varying the plate supply energ or by interruption of keying, and the like, where desired.

As above stated, filament current is supplied to the filaments of the tubes 172 and 173 from a source connected at 176, for example, and this current may then flow through the conductor 249, the choke 250, the switch 251 (assumin the switch to be in closed position) and t e conductor 252 to the connection 253 to the filament. In such case, with the switch 251 closed there would be a steady flow of current to the filament from the source 176 which might be smoothed by the choke 250, but with the switch 251 arranged in the open position, as shown, then current from the source connected at 176 may flow to the terminal 254 to which a pair of conductors 255 and 256 are connected. The conductors 255 and 256 are then each arranged through appropriate brushes to bear against the surface of a commutator, diarammatically shown as 257, which is rotated y any appropriate constant speed device, and which has thereon a conducting segment 258 and a non-conducting segment,259, each occupying one half the surface of the commutator.

Also connected to the commutator is a second pair of conductors 260 and 261 between which is a resistor 262. The conductor 261 then connects to a terminal 263 so as to supply filament current to the conductor 252. Thus, for example, in the position in which the commutator is shown, current from .the source connected at 176 may flow through the conductor 249, the choke 250, the terminal 254, the conductor 256 to the conducting portion 258 of the armature and then to the conduc tor 260, the resistor 262 and the conductor 261 through the terminal 263 and conductor 252 to the point of connection 253 to the filament of the tube 172. Due to the filament supply 

